If you’re more concerned about petrochemicals than having it done fast, I’ve heard a similar solution is to drill several deep holes into the stump, and then fill with … jam or jelly.
Supposedly, the sugars attract insects and other things that help decay the wood faster. But it’s hardly a quick solution. (Cheap, though.)
Dig it out.
Termites?
Is it a fence you share with a neighbor? If so, take into account any property line issues. Don’t assume that the fence is exactly on the property line. It may be set back on your neighbor’s side, in which case you may not be able to put your fence panel there without their permission.
But if there’s not a problem with you removing the stump, probably the fastest way is to rent an angle grinder and grind down the 2" that are sticking out. How dead is the stump? Many trees are resistant to being cut down and will continue to sprout back again and again. If that’s the case, then you’ll need to remove it completely or use chemicals to kill it or else the sprouts will push through your fence panel.
But then how will you anchor the prosthesis?
Har de HAR HAR. :dubious:
Okay, I must admit that * is* a good one 
make swiss cheese out of it with a half inch spade bit and then chop it up with an ax or maul.
I wish!
There are plenty of slow ways to get it out and will work. I’ve used the stump grinders before, still takes a while to get it below surface, but one of your best options. Unless you’re outside city limits, then I highly recommend picking up a lb of Tannerite placed into the stump which will make short work of it.